When regluing a wooden joint, for example, several important practical considerations arise. It is clearly desirable that the glue be applied under high pressure to insure that all small interstices of the joint are completely filled with fresh glue and that the glue be relatively quick drying, which usually requires a glue of relatively high viscosity, in turn increasing the pressure required for application. At the same time, relatively simple, wholly manually operated tools are desirable to maintain low costs and avoid need for a power source. Such tools should also be relatively compact and handy to use in confined spaces, as access to furniture joints can be very limited.
U.S. Pat. No. 2,040,126 issued to Grieve in 1935 teaches a procedure for regluing tenon and mortise joints in which a small pilot hole is bored through the tenon and a needle shaped nozzle of a glue gun is inserted into the hole and a charge of glue is forced therethrough to flow between the mortise and tenon in an attempt to fill the gaps therebetween.
However, the patent teaches the use of a manually operated, syringe-type gun which cannot apply a very high pressure to force the viscous glue through the small hole, limiting the speed and effectiveness of application. In addition, any attempt to increase the injection pressure in the prior device would increase the risk of glue being forced back along the hole between the pilot hole wall the nozzle exterior also limiting the effective pressure of glue application in the joint.
A later U.S. Pat. No. 3,352,336, issued to Smith in 1967, teaches a manually operated glue injector having a piston shaft threadingly attached to the glue reservoir cylinder and a nozzle having a self cutting thread which provides a seal with the pilot hole wall, so that rotation of the piston shaft enables a higher glue injection pressure to be obtained while the self cutting thread seals the pilot hole, obviating risk of glue leakage back along the hole past the nozzle as a result of back pressure.
However, clearly, the entire process is relatively slow as the entire gun carrying the glue must, at each joint, be carefully screwed into the hole and subsequently unscrewed therefrom, while the manual rotation of the piston required to obtain the higher pressure is also a relatively slow procedure increasing undesirably the application or set up time. This is particularly significant when all joints of one or more articles of furniture are to be reglued as, either the gun must carry only sufficient charge for a single application, which requires a time consuming refilling step for each joint, or the glue must remain in the gun for a relatively long period, undesirable with fast setting glues.
Furthermore, manipulating the entire gun adjacent the joint can prove inconvenient, as the gun is relatively cumbersome.
Needle-form nozzles currently used for regluing veneers are generally too short and of large diameter so that it is often difficult to penetrate the layers properly, while the bores are so large that they often become plugged with splinters.